Rancho Santa Margarita is a city in Orange County, California, United States. Take a look below for 15 fun and interesting facts about Rancho Santa Margarita, California, United States. 1. One of Orange County’s youngest cities, Rancho Santa Margarita is a master-planned community. 2. The population was 47,853 at the 2010 census, up from 47,214…